This invention relates to a mark position detecting apparatus for detecting the position of a mark written between two reference marks.
Conventionally, to effect an automatic facsimile transmission a document is provided at a prescribed place with a pattern region for designating the address or addresses to which a copy of document is to be transmitted. Generally, such a pattern region has one or more address marks which are bar codes or the like and is scanned by optical means. To obtain an electric signal corresponding to the pattern region a photo-electric converter is employed. In response to the electric signal, only the facsimile receiver or receivers which correspond to the address marks are set to receive the information from the transmission station.
FIG. 1 shows an example of a pattern region, which is positioned at the upper portion of document 1. This pattern region consists of two reference marks 2 and 3 of the same width and an address mark region 4 between the reference marks 2 and 3. The address mark region 4 is divided into address mark columns having the same width, the number of which is equal to or more than that of the necessary addresses. The address mark columns are separated from one another by, for example, dropout color lines. Any desired address mark column is at least partly painted out, for example, by hand to enter an address mark 5 in the address mark region 4.
To read out the marked address, the pattern region is scanned in the ordinary facsimile scanning direction. Then, a photo-electric converter generates such a pattern signal as shown in FIG. 2A, which indicates the position of the address mark 5 relative to the reference marks 2 and 3. In the meantime, a clock pulse generator produces such clock pulses of a specific frequency as shown in FIG. 2B. During the period of time between the trailing edge of a pulse corresponding to the first reference mark 2 and the leading edge of a pulse corresponding to the second reference mark 3, the pulses shown in FIG. 2B are supplied to a counter as shown in FIG. 2C. The count of the counter therefore corresponds to the position of the address mark 5, and is supplied as an address code to an automatic dialing device. As a result, the dialing device connects the desired facsimile receiver to the facsimile transmission station.
Such a conventional address designating system is applicable if about 20 and 30 address mark columns are provided on an A4-size original document so that each column may have a sufficient width of about 6 to 10 mm. But it cannot be applicable if the necessary address mark columns amount to 70 to 80. In this case the column width is as narrow as 2 to 3 mm, and it would occur that instead of a marked address mark column an unmarked one be erroneously read out for the following reason.
Assume now that in a fascimile transmitter, a document is placed on a flat table and the pattern region thereof is reduced in size and scanned by optical means, thereby to obtain a pattern signal. If, in this case, different facsimile transmitters of the same type are employed to work on the same document, the optical means scan the document inevitably at a different speed, however, finely they are adjusted. As a result, the scanning distance for a given time becomes longer or shorter by about 1 percent. This change of scanning distance causes a variation of the number of clock pulses which are counted during the period between the detection of the first reference mark 2 and the detection of the address mark 5. Consequently, the position of the address mark 5 cannot be detected correctly, and a wrong facsimile receiver is set to receive the information from the facsimile transmitter.
Further, a correct address designation is impossible if the document is placed slantwise on the flat table or contracts or expands due to a variation of the ambient humidity. If, for example, an A4-size document shrinks or expands by 1 to 2 percent of its original size, its pattern region becomes 2 to 4 mm shorter or longer. This makes it impossible to effect an accurate address designation in case the pattern region has as many as 70 to 80 address mark columns.